The sheet materials to which this invention is directed are usually referred to in the art as "electrical" silicon steels or, more properly, silicon-irons and are ordinarily composed principally of iron alloyed with about 2.2 to 4.5 percent silicon and relatively minor amounts of various impurities and very small amounts of carbon. These products are of the "cube-on-edge" type, more than about 70 percent of their crystal structure being oriented in the (110) [001] texture, as described in Miller Indices terms.
Such grain-oriented silicon-iron sheet products are currently made commercially by the sequence of hot rolling, heat treating, cold rolling, heat treating, again cold rolling and then final heat treating to decarburize, desulfurize and recrystallize. Ingots are conventionally hot-worked into a strip or sheet-like configuration less than 0.150 inch in thickness, referred to as "hot-rolled band." The hot-rolled band is then cold rolled with appropriate intermediate annealing treatment to the finished sheet or strip thickness usually involving at least a 50 percent reduction in thickness, and given a final or texture-producing annealing treatment.
As disclosed and claimed in U.S. Pat. No. 3,905,842, issued Sept. 16, 1975, to Herbert E. Grenoble and assigned to the assignee hereof, the magnetic properties of such sheet materials can be very considerably improved by incorporating boron in the metal so that it is present there in critical proportion to the nitrogen content of the metal at the time of the final or texture-developing anneal. As stated in that patent, the amount of boron required to produce that result is quite small but highly critical.
Similarly, it is disclosed in U.S. Pat. No. 3,905,843, issued Sept. 16, 1975, to Howard C. Fiedler and assigned to the assignee hereof, that such use of boron in the metal in proportion to nitrogen while maintaining the ratio of manganese to sulfur at less than 2.1 will enable the corresponding substantial improvement in magnetic properties of a product made by the process including cold rolling in two stages, including an intermediate anneal.
Still another related disclosure concerning the use of small but critical amounts of boron in silicon-iron is set forth in U.S. Pat. No. 3,957,546, issued May 18, 1976 Howard C. Fiedler and, assigned to the assignee hereof, which is directed to the novel concept of cold rolling hot-rolled silicon-iron sheet directly to final thickness without an intermediate heat treatment through the use of small but critical amounts of boron and by maintaining the ratio of manganese to sulfur in the metal at less than 1.8.